The invention relates generally to clutches and more specifically to a ball ramp clutch having a force amplifying configuration which has application in motor vehicle drive line components.
Friction clutch packs find application in a broad range of power and torque transfer systems. Such clutch packs require a force parallel to the axis of the clutch pack to clamp the multiple interleaved friction plates together to transfer rotary power. The torque transmitted at any friction surface is equal to the clamping force at the interface times the mean radius of the friction surface. To increase the torque throughput of such a clutch, the mean radius of the clutch plates may be increased, additional plates may be added or the compressive force may be raised.
Increasing the mean radius of the friction plates is often an unworkable solution as the available space for a clutch, particularly in motor vehicle drive line components may be tightly constrained. Increasing the number of clutch plates is subject to a law of diminishing return due to the axial sliding friction generated within the clutch pack.
The foregoing suggests that increasing the force applied to the clutch pack may be the most convenient manner of increasing the torque throughput of a clutch. However, generation of a greater compressive force typically requires a larger, heavier, more expensive and typically slower acting force generator. This situation, in turn, suggests that the easily stated goal of increasing torque throughput through a multi-plate friction clutch pack when the design constraints include exterior size and operator weight and speed render improvement more challenging. The present invention is directed to improvements in ball ramp multi-plate friction clutches which improve torque throughput and performance.
A preferred embodiment compound ball ramp clutch assembly for motor vehicle drive line components includes a force amplifying assembly having two ball ramp operators arranged in tandem. The clutch assembly includes a first ball ramp operator having opposed cam plates with load transferring balls, an electromagnetic coil, a rotor and an armature. When energized, the coil creates drag which causes separation of the plates of the first ball ramp operator which compresses a primary (pilot) clutch pack disposed in mechanical parallel with the cam plates and load transferring balls of a second ball ramp operator. A speed difference and drag across the second ball ramp operator compresses a secondary (main) clutch pack. Significantly increased torque carrying capacity is exhibited by such a compound or tandem ball ramp clutch assembly. In an alternate embodiment, the electromagnetic coil and first ball ramp operator are replaced by a hydraulic operator assembly.
Thus it is an object of the present invention to provide a multi-plate friction clutch having tandem ball ramp operators providing increased torque throughput.
It is a further object of the present invention to provide a multi-plate friction clutch having increased torque throughput for use in motor vehicle drive line components such as transfer cases and differentials.
It is a still further object of the present invention to provide a multi-plate friction clutch having an electromagnetic or hydraulic operator and primary and secondary clutch packs acted upon by respective operators.
It is a further object of the present invention to provide a multi-plate friction clutch assembly having electromagnetic or hydraulic operators which actuate respective ball ramp operator assemblies.
Further objects and advantages of the present invention will become apparent by reference to the following descriptions of the preferred and alternate embodiments and appended drawings wherein like reference numbers refer to the same component, element or feature.